1. Field of the Invention
This invention relates to a PWM inverter for obtaining a PWM (pulse-width-modulated) rectangular wave from a DC power source by time ratio control, and more particularly, to a PWM inverter having switching means to apply a DC voltage across a main circuit, comprising a series circuit of a main winding and a resistor, by time ratio control with the polarity of the applied voltage inverted alternately.
More specifically, this invention relates to a PWM inverter that accomplishes on-off control of the aforementioned switching means by a saturable transformer using a saturable core.
2. Description of the Prior Art
In the conventional switching power source which obtains a sinusoidal (AC) output or a stabilized DC output from a DC power source by time ratio control of switch elements, control of changeover of the aforementioned switch elements has been based on generating a pulse-width-modulated control signal of a constant frequency by a PWM controller. Such a controller is constructed by electronic circuit components such as integrated circuits, etc. The power of this control signal is amplified through use of electronic circuit based semiconductor elements, etc. The on-off operation of the switch elements is directed by this amplified control signal (see B. D. Bedford et al: Principles of Inverter Circuits (1964) pp 310-313, John Wiley & Sons, Inc.).
As a result, the conventional unit has the disadvantages that not only the construction of the PWM controller and the switch element drive circuit is complex but also the power loss of the switch element drive circuit increases when the switching frequency is increased.